The present invention relates to a line type ink-jet printer which has a line-type head in which a plurality of nozzles are arranged, whose length is corresponding to the width of the recording medium, and in which ink is jetted from the nozzles onto the recording medium, and the recording medium is conveyed in a subsidiary scanning direction to thereby from an image is formed on the recording medium. More particularly, the present invention relates to an ink-jet printer suitable for high speed image formation and image formation with high resolution.
The image formation in the ink-jet printer is carried out as follows: the head is moved in the primary scanning direction while droplets of ink which are jet-controlled by an image signal, are jetted from nozzles of the head onto the recording medium; when the image is recorded on the recording medium by one line, the recording medium is moved in the subsidiary scanning direction by one line; the droplets of ink are jetted again from nozzles of the head onto the recording medium and one line of image is formed; and hereinafter, by repeating these operations, an image is formed on the recording medium.
Alternatively, as another structure, as disclosed in Japanese Tokkaisho No. 62-161547, there is a structure in which ink nozzles of the head are arranged with an equal pitch in the length of almost maximum recording width of the recording medium, and the head is structured as a fixed linetype head.
According to the structure, movement of the head in the primary scanning direction is not necessary, and an image can be formed only by the conveyance of the recording medium in the subsidiary scanning direction which is perpendicular to the primary scanning direction, thereby, high speed image formation can be carried out.
As described above, in the ink-jet printer having a fixed line-type head in which the head is not moved in the primary scanning direction, for example, when there are such nozzle defects as in the cases in which nozzles are blocked by dusts or the like, and ink can not be jetted (hereinafter, called no-jetting of ink), or the peripheral portion of a jetting port of the nozzle is wetted by ink, a liquid drop of the jetted ink is attracted to the wetted portion, and the ink is not recorded on the target position on the recording medium (hereinafter, called curved-shooting of ink), image failure is generated in the image formed on the recording medium.
In more detail, in the case of no-jetting of ink, a longitudinal streak is formed on the recording medium in the subsidiary scanning direction. Further, in the case of the curved-shooting of ink, as shown in FIG. 12, when the jetted ink C from the nozzle c causes the curved-shooting of ink due to wetting of ink on the periphery of the nozzle and forms a line Cxe2x80x94C, the line Cxe2x80x94C formed by dots of the jetted ink approaches a line Bxe2x80x94B formed in the same manner, and simultaneously, is apart from a line Dxe2x80x94D, and a pitch between lines with respect to other lines Axe2x80x94A and Exe2x80x94E is different, and a longitudinal stripe is formed as the image formed by dots of ink in the subsidiary scanning direction.
When such the image failure due to a defect of the nozzle occurs, the image failure can not be solved if the head is not replaced.
FIG. 20 is a view showing an example of a line type ink-jet printer having the conventional line-type head.
In the line type ink-jet printer 1, the recording sheet P is nipped by conveyance roller pairs 31 and 32, and is further conveyed in the direction Y in the drawing, by the roller pair 31 driven by a conveyance motor 33.
A line-type head 2 is provided in opposite to the surface PS of the recording sheet P as the recording medium between conveyance roller pairs 31 and 32. The line-type head 2 is connected to a control substrate 51 on which the control section is provided, through a flexible cable 4 (hereinafter called FPC).
Next, referring to FIG. 2, the line-type head will be described.
As shown in the drawing, the line-type head 2 can be separated into a base substrate 24 and a cover substrate 25. Piezoelectric elements 22 are arranged in a line on the base substrate 24, and each piezoelectric element 22 is connected to the FPC 4 through a circuit lead 23.
Nozzles 21, each of which form a pair with each piezoelectric element 22, are aligned on the cover substrate 25 in a line with the same pitch, each nozzle 21 is connected to a fine tube provided with a portion to receive ink-jet-pressure by the piezoelectric element 22, and the fine tube is connected to an ink tank provided in the cover substrate 25.
Next, operations of the above-described structure will be described. A control section on the control substrate 51 makes a conveyance mechanism 3 convey the recording sheet P at a predetermined speed, drives the piezoelectric element 22 according to an image signal, jets liquid drops of ink simultaneously for each line from the nozzles 21 of the line-type head 2, and forms an image on the recording sheet P.
As compared to a so-called shuttle type ink-jet printer whose head is driven in the primary scanning direction, the line type ink-jet printer with the above-described structure does not need the movement of the head in the primary scanning direction, and can form an image only by the conveyance of the recording sheet P in the subsidiary scanning direction which is perpendicular to the primary scanning direction, thereby, the line type ink-jet printer can conduct high speed image formation.
However, in such the line type ink-jet printer having only one line-type head 2, for example, when there are such defects of the nozzle 21 as in the cases in which the nozzles 21 of the line-type head 2 are blocked by dusts or the like, and ink can not be jetted (hereinafter, called no-jetting of ink), or the peripheral portion of a jetting port of the nozzle 21 is wetted by ink, a liquid drop of the jetted ink is attracted to the wetted portion, and the ink is not recorded on the target position on the recording medium (hereinafter, called curved-shooting of ink), an image failure (noise) occurs in the image formed on the recording sheet P, which is a problem.
Further, it is necessary to provide piezoelectric elements 22, ink tanks, fine tubes, etc., in the line-type head 2 corresponding to each nozzle 21, therefore, there is a limit to make a pitch of the nozzle 21 closer, thereby, an image with high resolution can not be obtained, which is also a problem.
In this case, when the line-type head 2 is slantingly arranged to the primary scanning direction, a pitch of the nozzle in the primary scanning direction is made closer, and the resolution can be increased, however, the distance to move the recording sheet P in the subsidiary scanning direction is increased, and image forming speed is lowered, which is another problem.
Further, the ink-jet head has a proper driving frequency, without depending on its type such as the type using piezoelectric elements, the high voltage system, the bubble-burst type, etc.
Accordingly, there is such a problem that the image forming speed is also determined by the driving frequency of the head.
Further, when a line-type head is produced, in the present, cost is increased for the production of the line-type head longer than 5 inches, accordingly, a plurality of short line-type heads are jointed and one longer line-type head is produced.
On the other hand, in the line-type head, liquid drop jetting characteristics of both end nozzles which are affected by only one side nozzle, and liquid drop jetting characteristics of nozzles except both ends which are affected by both side nozzles, are different from each other.
Accordingly, in the line-type head produced by jointing short line-type heads, nozzles having different liquid drop jetting characteristics exist in one line, there is also a problem that image failure occurs on the recording sheet P.
Further, when the line-type head is produced by jointing short line-type heads, it is difficult to correctly adjust nozzle pitches at joint portions, accordingly, this is also a problem to cause image failure on the recording sheet P.
The present invention is achieved in view of the foregoing problems.
The first object of the present invention is to provide an ink-jet printer by which high speed image formation can be carried out.
The second object of the present invention is to provide a line type ink-jet printer in which image failure due to a defective nozzle can be improved.
The third object of the present invention is to provide a line type ink-jet printer in which the frequency of replacement of a line-type head is reduced, replacement cost is reduced, and an increase of reliability can be attained.
The fourth object of the present invention is to provide an ink-jet printer by which image formation with high image quality can be carried out.
To overcome the cited shortcomings, the abovementioned objects of the present invention can be attained by an ink-jet printer described as follow:
(1) An ink-jet printer, comprising:
a first printing head to emit ink particles, being a line-type head in which a plurality of ink-jet nozzles are arranged in a line; and
a second printing head to emit ink particles having a color same as that of the ink particles emitted by the first printing head.
(2) An ink-jet printer, comprising:
a printing head to emit ink particles, being a line-type head in which a plurality of ink-jet nozzles are arranged in a line;
a nozzle checking means for detecting a defect of the ink-jet nozzle mounted in the printing head; and
a driving means for moving the printing head in a direction of the line,
wherein the ink-jet printer performs a plurality of scanning operations onto a same scanning line of the recording medium to form an image of the scanning line when the nozzle checking means detects the defect, in such a manner that, in at least one scanning of the plurality of scanning operations, the driving means moves the printing head in a direction of the line so as to form the image of the scanning line by using another normal ink-jet nozzle instead of a defective ink-jet nozzle detected by the nozzle checking means.
Further, in order to solve the above-described problems and to attain the abovementioned objects, the following features of an ink-jet printer are desirable embodiments of the present invention.
(1) A line-type ink-jet printer which comprises,
a line-type head in which a plurality of ink-jet nozzles are arranged in a width direction substantially the same length as that of a recording medium, to emit ink particles from the ink-jet nozzles onto the recording medium, wherein the line-type ink-jet printer forms an image on the recording medium by conveying the recording medium in a subsidiary scanning direction, and further comprises,
a nozzle checking means for detecting a defect of said ink-jet nozzle included in said first printing head;
a auxiliary head arranged in parallel with the line-type head; and
a control means for conducting image formation by means of the auxiliary head when a defect of the ink-jet nozzles included in the line-type head is detected by information incoming from the nozzle checking means.
As described above, when there is any defect on the line-type head, image failure due to nozzle defect can be improved by conducting image formation by using an auxiliary head provided in parallel to the line-type head.
Herein, when a head having image recording width more than that of the line-type head is used as an example of an auxiliary head, image failure can be improved by using the auxiliary head instead of the line-type head, or by driving a nozzle of the auxiliary head corresponding to the defective nozzle of the line-type head.
Particularly, when a nozzle of the auxiliary head is driven corresponding to the defective nozzle of the line-type head, frequency of the replacement of the line-type head is decreased, resulting in a decrease of the replacement cost, and an increase of the reliability.
Further, when, as the auxiliary head, a head movable in the line direction of the line-type head is used, the auxiliary head is moved in such a manner that a nozzle of the auxiliary head is located at a position corresponding to the defective nozzle of the line-type head, the nozzle of the auxiliary head is used instead of the defective nozzle of the line-type head, and an image is formed, thereby, image failure is improved and frequency of replacement of the line-type head is reduced, resulting in a reduction of replacement cost and an increase of the reliability.
(2) A line-type ink-jet printer which comprises,
a line-type head in which a plurality of ink-jet nozzles are arranged in a width direction substantially the same length as that of a recording medium, to emit ink particles from the ink-jet nozzles onto the recording medium, wherein the line-type ink-jet printer forms an image on the recording medium by conveying the recording medium in a subsidiary scanning direction, and further comprises,
a nozzle checking means for detecting a defect of said ink-jet nozzle included in said first printing head;
a driving means for moving the line-type head in the line direction,
wherein said ink-jet printer performs a plurality of scanning operations onto a same scanning line of the recording medium to form an image of the scanning line when a defect of the ink-jet nozzles included in the line-type head is detected by information incoming from the nozzle checking means, in such a manner that, in at least one scanning of the plurality of scanning operations, the driving means moves the line-type head in the line direction so as to form the image of the scanning line by using another normal ink-jet nozzle instead of a defective ink-jet nozzle detected by the nozzle checking means.
In the plurality of image formation conducted on the same recording medium, at least one image formation is conducted by moving the line-type head in the line direction of the line-type head, and image formation of the defective portion is conducted by using other normal nozzles, thereby, image failure due to the defect of the nozzle can be improved.
Further, frequency of replacement of the line-type head is reduced, resulting in a reduction of replacement cost and an increase of the reliability.
Incidentally, from a view point of the mechanical simplicity, it is desirable that the drum, rotated around its center axis, conveys said recording medium in a subsidiary scanning direction by bearing the recording medium on its circumferential surface.
(3) An ink-jet printer, in which
a plurality of line-type heads, each of which emit ink particles having a same color each other onto a recording medium, are arranged.
A plurality of line-type heads by which liquid drops of ink of the same color are jetted on the recording medium, are provided, thereby, image formation with high image quality or high speed image formation can be attained.
(4) The ink-jet printer of item (3), in which, between adjacent nozzles of one line-type head of the plurality of heads, nozzles of the other line-type heads are located.
In the primary scanning direction, when, between adjacent nozzles of one line-type head of the plurality of heads, nozzles of the other line-type heads are located, resolution in the primary scanning direction is improved, and a high quality image can be formed.
Further, even if there is a nozzle defect such as no-jetting of ink or curved-shooting of ink, in any line-type heads of a plurality of line-type heads, and noise is generated in an image, the noise is reduced by image formation by using other line-type heads, and high image quality is attained.
For example, when an arrangement pitch of nozzles in a primary scanning direction of each line-type head and a number of the line-type heads are defined as P(dpi) and N, respectively, the resolution of the formed image is resulted in Pxc3x97N (dpi) by shifting an arrangement of nozzles of each line-type head at P/N(dpi) in a primary scanning direction. Thus the resolution is improved and high image quality is attained.
(5) The ink-jet printer of item (3), in which
a plurality of line-type heads are arranged in a direction so that each line of the line-type heads crosses the primary scanning direction.
When a plurality of line-type heads are located in the direction to cross the primary scanning direction, nozzle pitches in the primary scanning direction are decreased, resolution is increased, and image formation with high quality can be attained.
Further, by providing a plurality of line-type heads, the movement distance of the recording sheet in the subsidiary scanning direction is decreased, and the image forming speed is not lowered.
(6) The ink-jet printer of item (3), in which
each of nozzles of the plurality of line-type heads is located at the same position in the primary scanning direction.
When each of nozzles of the plurality of line-type heads is located at the same position in the primary scanning direction, a plurality of line images can be simultaneously formed, thereby, high speed image formation can be attained.
Further, when the relative movement in the subsidiary scanning direction of the recording sheet to line-type heads is made into such a movement that a band image obtained by one image formation by a plurality of line-type heads, overlaps, noises due to no-jetting of ink, or curved-shooting of ink are decreased in one line-type head, and a high quality image can be formed.
Still further, in the case where each line-type head is produced by jointing short line-type heads, when joints of small line-type heads of each line-type heads are respectively shifted in the primary scanning direction, image failure generated when short line-type heads are jointed, can be prevented.
(7) The ink-jet printer of item (3), which comprises,
a plurality of line-type head groups including a plurality of line-type heads in which each nozzle of each line-type head is located at the same position in the primary scanning direction,
wherein, between adjacent nozzles of one line-type head group of the plurality of head groups, nozzles of the other line-type head groups are located.
In the line-type head group, each nozzle of each linetype head is located at the same position in the primary scanning direction, thereby, a plurality of line images can be simultaneously formed, resulting in high speed image formation.
Yet further, when the relative movement in the subsidiary scanning direction of the recording sheet P to line-type head groups is made into such a movement that a band image obtained by one image formation by a plurality of line-type head groups, overlaps, noises due to no-jetting of ink, or curved-shooting of ink are decreased in one line-type head group, and a high quality image can be formed.
In the case where each line-type head is produced by jointing short line-type heads, when joints of small line-type heads of each line-type heads are respectively shifted in the primary scanning direction, image failure generated when short line-type heads are jointed, can be prevented.
Furthermore, when, between adjacent nozzles of one linetype head group of the plurality of head groups, nozzles of the other line-type head groups are located, resolution in the primary scanning direction is improved, and a high quality image can be formed.
Further, even if there is a nozzle defect such as no-jetting of ink or curved-shooting of ink, in any line-type head of a plurality of line-type heads, and noise is generated in an image, the noise is reduced by image formation by using other line-type heads, and high image quality is attained.